A number of methods for the demonstration and determination of antigens and antibodies are already known, such methods making use of the immunological affinity between these components.
When using labelled components, one of the best known methods is the so-called Sandwich technique, in which, for the demonstration and determination of, for example, an antigen in a test-fluid, this antigen is incubated with a certain quantity of labelled, for example, radioactive antibody directed against this antigen, and with a certain quantity of an antibody, rendered insoluble, also directed against the antigen to be determined. After termination of the immunological reaction, the radioactivity in the liquid or solid phase is measured, the said radioactivity being a measure of the amount of the antigen to be determined.
This method, just as the other customary techniques, has the major disadvantage that one of the reaction components in the main reaction of this immunological estimation is in an insoluble form, as a result of which the affinity for the binding partner decreases, and the sensitivity and accuracy of the test system are, therefore, adversely affected.
In order to increase the sensitivity, this insoluble component ought to be used in relatively large quantitites, which is a major disadvantage for economic reasons, since most antibodies are particularly expensive.
An immunological method for the demonstration and determination of antigens and antibodies, in which the reaction between antigen and antibody is a reaction of soluble components, such that the sensitivity is considerably increased, and in which a separation into solid and liquid phases, by using an insoluble immunoadsorbent, is still obtained, has now been found; although the method is immunologically specific for one of the reaction components it is still possible to make an arbitrary choice within a certain group of substances.